1. Field of the Invention
The present invention relates generally to endovascular devices for capturing particulate during vascular procedures and methods for making same. More particularly, the invention relates to a distal protection element located at the distal end of a delivery member prevent emboli in a blood vessel from moving away from the treatment site during a vascular procedure. The distal protection element is comprised of filaments, some of which have been reduced in thickness during manufacture of the device, so that the device has a low collapsed profile and greater flexibility in the end regions.
2. Related Art
A variety of treatments exist for compressing or removing athersclerotic plaque in blood vessels. The use of an angioplasty balloon catheter is common in the art as a minimally invasive treatment to enlarge a stenotic or diseased blood vessel. This treatment is known as percutaneous transluminal angioplasty (hereinafter, “PTA”). To provide radial support to the treated vessel in order to prolong the positive effects of PTA, a stent may be implanted in conjunction with the procedure.
Thrombectomy is a minimally invasive technique for removal of an entire thrombosis or a sufficient portion of the thrombosis to enlarge a lumen of a stenotic or diseased blood vessel and may be accomplished instead of, or in addition to, a PTA procedure. Atherectomy is another well-known minimally invasive procedure that mechanically cuts or abrades a stenosis within a diseased portion of the vessel. Alternatively, ablation therapies use laser or RF signals to superheat or vaporize the thrombosis within the vessel. Particulate debris loosened during such procedures may be removed from the patient through the catheter.
During each of these procedures, there is a risk that particles dislodged by the procedure will migrate through the circulatory system to embolize distally and cause infarction or strokes. Thus, practitioners have approached prevention of escaped emboli through use of distal protection elements such occlusion devices and filters as well as lysing and aspiration techniques. For example, it is known to remove the particulate material by suction through an aspiration lumen in the treatment catheter or by capturing debris in a filter or occlusion device positioned distal of the treatment area.
Prior art temporary distal protection elements such as filters or occlusion devices are associated with either a catheter or guidewire and are positioned downstream of the area to be treated. One prior art filter arrangement includes a dilatation balloon and a filter mounted on the same catheter. The filter is located distal to the dilatation balloon and consists of a filter material secured to resilient ribs. A filter balloon is located between the catheter exterior and the ribs. Inflation of the filter balloon extends the ribs outward across the vessel to form a trap for fragments loosened by the dilatation balloon. When the filter balloon is deflated, the resilient ribs retract against the catheter to retain the fragments during withdrawal of the catheter.
Another prior art device provides an expandable occlusion member mounted on a slender, elongate wire. The occlusion member is placed distal to the intended treatment site and expanded to obstruct the flow of bodily fluids during the procedure. An interventional catheter is guided to the treatment site over the wire and the vessel narrowing is enlarged. Any emboli produced are trapped upstream of the occlusion balloon. Bodily fluid containing the particulate is aspirated from the vessel, either through a dedicated lumen in the treatment catheter, or via a separate aspiration catheter that has been exchanged for the treatment catheter. The occlusion member is then collapsed and removed from the patient. The occlusion member may be an inflatable balloon or a mechanically expandable structure covered by a non-porous membrane.
Another prior art device includes a filter mounted on the distal portion of a hollow guidewire or tube. A moveable core wire is used to open and close the filter. The filter is secured at the proximal end to the tube and at the distal end to the core wire. Pulling on the core wire while pushing on the tube draws the ends of the filter toward each other, causing the filter framework between the ends to expand outward into contact with the vessel wall. Filter mesh material is mounted to the filter framework. To collapse the filter, the procedure is reversed, i.e., pulling the tube proximally while pushing the core wire distally to force the filter ends apart.
Another prior art device has a filter made from a shape memory material. The device is deployed by moving the proximal end of the filter towards the distal end. The filter is collapsed by sliding a sheath over the filter and then withdrawn by removing the sheath and filter together.
Another prior art filter device includes a compressible polymeric foam filter mounted on a shaft that is inserted over a guidewire. The filter is inserted in a collapsed state within a housing which is then removed to deploy the filter once in position. The filter is retracted by inserting a large bore catheter over the shaft and the filter and then removing the shaft, filter and catheter together.
Another prior art filter arrangement has a filter comprised of a distal filter material secured to a proximal framework. This filter is deployed in an umbrella manner with a proximal member sliding along the shaft distally to open the filter and proximally to retract the filter. A large separate filter sheath can be slid onto the shaft and the filter can be withdrawn into the sheath for removal from the patient.
Other known prior art filters are secured to the distal end of a guidewire with a tubular shaft. Stoppers are placed on the guidewire proximal and distal of the filter, allowing the filter to move axially independently of the guidewire. Sheaths are used to deploy and compress the filter.
One problem with known filter arrangements is that the capture element has a large profile as measured at the distal and proximal end regions thereof. The large profile of the collapsed capture element creates stenosis-crossing problems and possible snagging as the capture element is withdrawn through a stent. In addition, the force required to pull the capture element back into the retrieval sheath is greater than that which would be required if the capture element had a smaller profile. In particular, the braided element is too thick at the end regions under the marker bands. Further, the braided element is too thick in the tapered portion of the end regions, causing these regions to resist lying snugly about the guidewire when collapsed. In other words, the end regions may bulge outwardly instead of collapsing flatly against the core wire.
The main factor contributing to the enlarged profile of the filter or capture element is the thickness of the filaments used to form the filter. The profile is increased in part because the filaments are grouped together in a relatively small area for connection to the core wire and the thickness of the filaments prevents an appropriate reduction in profile.